At least one hard disk drive (HDD) is used in almost all computer system operations. In fact, most computing systems are not operational without some type of HDD to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the HDD is a device which may or may not be removable, but without which the computing system will generally not operate.
A typical HDD uses an actuator assembly to move magnetic heads so as to write or read data on the desired location in the disk assembly. During this operation, the disk assembly is rotated at predetermined revolutions per minute (RPMs). It is not uncommon for a hard disk drive to operate at speeds of up to 15,000 RPMs at the current state of the art. Airflow inside HDD's generated by the rotational motion of disk assembly results in the vibration in HDD's components. The flow-induced vibration in an HDD system causes what is commonly known as track misregistration (TMR) which is a measurement used to determine the acceptability of errors during data reading and writing process. The severity of flow-induced vibration depends upon geometrical factors used inside an HDD. It is often characterized by the Reynolds number which is proportional to the characteristic speed of the spinning disk (such as the linear speed at the outer diameter of the disk) and the characteristic dimension (such as disk diameter, disk spacing, or any geometrically meaningful length). In order to achieve acceptable level of TMR, it is important to lower the level of excitation during servo pattern writing process. It is a common practice that a somewhat lower rotational speed is used in the servo writing process in order to help lessen the severity of flow-induced vibration. Even as such, the airflow can cause movable components inside the drive to shift relative to each other, including the magnetic disk stack to tilt or the read and write heads to sway relative to each other. This movement leads to improper alignment and produces errors in writing reference servo tracks on the magnetic disks.